My Yamaha 300 has 280 hours and still under warranty. At about 30 hours, a stalling problem started. When bringing the boat up to speed at a normal range, it will stall between 1800 and 2200 RPM. It will also do the same when bringing the speed down. I have had the boat back for service way too many times but problem still persists. service department has tried hooking up shop tank and it still continues to stall. Engine will start up immediately after stall. Any suggestions?